1. Field of the Invention
The invention relates to laminated materials and particularly to a room-temperature dry process for texturing copper on plastic to improve adhesion of coatings to the copper surface through mechanical as well as chemical bonding.
2. Description of the Prior Art
Copper surfaces are generally inappropriate for adhesion of additional materials because of the smoothness of the copper surfaces, as well as the resistance of copper to chemical reaction. If it should be desirable to laminate copper with a plastic material it is desirable to provide mechanical as well as chemical bonding wherever possible.
Abrasive techniques are known for increasing the surface area and providing a mechanical bond through mechanical locking of copper to plastic.
Wet etching techniques are also known to etch the surface of copper for increasing the surface area for mechanical bonding. See, for example, USSR Author's Certificate No. 530486, Maximov and Fedorov, "Precision Etching of Copper--by dipping in iodine and potassium iodide solution followed by ammonia solution."
Wet etching techniques are inherently messy and subject to contamination from the etching bath, and in most situations require electrical contact.
Purely chemical treatment of plastic has been described, so as to achieve an interface layer which sticks to the plastic and to which succeeding layers will adhere. See, for example, U.S. Pat. No. 3,445,264, Haines, "Method and Composition for Treating the Surface of Polymeric Articles to Improve Adhesion," May 20, 1969. This type of approach is impractical in situations where a pattern of copper is to be covered with a layer of plastic in a sandwich plastic-copper-plastic, because of electrical short circuit problems as well as plastic-plastic and plastic-copper adhesion problems.
Iodine ions are known in the context of high intensity ion bombardment. See, for example, U.S. Pat. No. 4,264,813, Chandrashekhar et al, "High Intensity Ion Source Using Ionic Conductors," Apr. 28, 1981. Ion bombardment, while very useful in environments where required, is a different mechanism (essentially mechanical in nature) from the chemical mechanism of this invention. Other ions (for example, xenon ions) have been reported with similar texturizing effect. See, for example, Hudson, "Ion Beam Texturing," J. Vac. Sci. Technol. Vol. 14, No. 1, January/February 1977, pp. 286-289. Seed materials such as tungsten or aluminum oxide are commonly required in such ion beam processors, and accelerating potentials in the range 500-2000 V are required.
Copper texturizing by sputter etching has been described, at equilibrium temperatures above 300.degree. C., in vacuo with argon at 300.degree. V. See, for example, Curmi and Harding, "Surface Texturing of Copper by Sputter Etching With Applications for Solar Selective Absorbing Surface," J. Vac. Sci. Techno., V. 17, No. 6, November/December 1980, pp. 1320-1325. See also Cuomo, Ziegler and Woodall, Appl. Phys. Lett. 26, 557 (1975). Such copper texturizing is not appropriate for accompanying plastics because of the high temperatures.